Modulation of nutritional and biochemical status of hydroponically grown Cucurbita pepo L. by Calcium Nitrate under saline conditions

: Salinity is one of the critical environmental factors that decreases the water availability and induces nutritional imbalance in crops. In order to study the effect of calcium nitrate [(Ca(NO 3 ) 2 ] in the nutrient solution under salinity conditions, an experiment was designed with different salinity (0, 50, and 100 mM) and Ca(NO 3 ) 2 (2, 3, and 4 mM) levels on Cucurbita pepo (zucchini). Based on the results, an increase in the salinity from 0 to 100 mM caused a decrease in the leaf potassium and calcium concentration, whereas the iron, magnesium and zinc concentrations increased. The most effective Ca(NO 3 ) 2 level in increasing the nutritional quality and yield of zucchini was 3 and 4 mM. Salinity at 50 and 100 mM significantly increased the leaf sodium concentration and leaf area as well as the leaf number per plant, while the application of both Ca(NO 3 ) 2 levels modulated the harmful effects of salinity. The amount of malondialdehyde (MDA), proline and hydrogen peroxide (H 2 O 2 ) as well as the catalase (CAT) activity increased under the severe salinity conditions, whereas the application of 4 mM Ca(NO 3 ) 2 had the potential of removing the negative effects of severe salinity. The catalase activity increased along with the increase in the Ca(NO 3 ) 2 concentration, which was independent from the salinity level. However, the amount of proline, MDA and H 2 O 2 decreased in plants fed with 3 and 4 mM Ca(NO 3 ) 2 compared to the control in the presence of salinity. These findings suggest that both the 3 and 4 mM concentrations of Ca(NO 3 ) 2 under 50 mM salinity could be used to improve the zucchini performance by maintaining the ion homeostasis and inducing the antioxidant defence system.